Means for producing high vacuum



Patented Mar. 27, 1934 UNiTa stares 1,952,717 MEAN S FOR PRODUCING HIGHVACUUM Ernest Anton Lederer,

East Orange, N. J., as-

signcr, by mesne assignments, to Radio Corporation of America, New York,N. Y., a corporation of Delaware No Drawing. Application January 8,1932, Serial No. 585,635

12 Claims.

This invention relates to an improved form of getter material such ascustomarily employed as a clean-up agent during the process ofevacuating electron devices.

I have heretofore employed a method of cleaning up residual gases of anelectron device by introducing into the envelope thereof a gettermaterial comprising an alloy consisting essentially of aluminum and analkaline earth metal, more particularly barium. The aluminum functionsprimarily as a protective'carrier (in the sense that it affords chemicalrather than physical protection) for the barium.

The getter is introduced into the device in a 15 solid form at the timeof sealing the mount into the envelope and may be supported by theelectrode structure or secured independently thereof.

After the usual mechanical evacuation of theenvelope, the alloy isflashed at a temperature not substantially higher than thevolatilization point of the barium.

Previous to the aforesaid practice it had been proposed to employ analloy of magnesium and barium containing a preponderance of magnesium asa getter material, but because of the comparative low volatilizationpoint of the magnesium it was difficult to determine when the barium wasflashed because the magnesium flash predominated, which quicklymanifested itself in the form of an opaque depositupon the interior ofthe envelope, thus making it impossible to observe when the. barium Wasflashed.

Since barium, due to its chemical activity, is

probablythe best clean-up agent which'can be 5 usedfor vacuum tubes andsimilar devices, it is It is an objectof my invention to preserve all ofthe advantages obtained by a barium flash without introducingundesirable complications. It is another object of my invention toprovide a method of cleaning up the residual gases of an electron deviceby reducing or eliminating :heat losses due to convection prior'toflashing the principal clean-up agent of the getter material.

Other objects having to do with the employment of a superior gettermaterial of which barium is the most effective clean-up constituent,will manifest themselves upon a reading of the following specification.

The specific improvement of the present invention over the abovementioned prior practice is the addition of a small percentage ofmetallic magnesium to a getter material, comprising an alloy of aluminumand an alkaline earth metal such as barium. This percentage of magnesiummay vary from about 1% to about 10% but I have obtained excellentresults with about 5% of magnesium added to an alloy consisting ofaluminum and barium, the barium constituting about 45% of the alloy.However, the barium content may be varied fromabout 5% to about 60%,depending upon the desired stabilityv of the getter material, which inturn depends upon the time required to process a receiving tube or thelike under existing factory conditions, it being obvious that the longerthe period required to complete the processing, a corresponding decreasein the percentage of barium should be used.

The magnesium in powdered form may be added to the powderedbarium-aluminum alloy and the mixture pressed up into pellets. Or byusing a suitable binder as a vehicle for the powdered alloy and themagnesium a mixture is obtained which can be used as a paste getter" forapplication to the electrodes or to a special holder designed to carrythe getter. If the getter material is in pellet form, the pellets may beattached They are quite stable in air and can successfully resistoxidation or contamination by moisture for a substantial period of time.

In heating up the getter material by any suitable means, such as with agiven high frequency source: the temperature of the getter material isconsiderably aifected by a small amount of gas. The reduction of the gaspressure by a few microns increases the temperature of the gettercarrier considerably. The magnesium metal, being the first constituentof the clean-up agent to flash, will lower the gas pressure. Thus thetemperature of the getter carrier can easily be brought up to about 930C. at which point the barium-aluminum alloy will melt and the bariummetal will readily volatilize. The percentage of the magnesium is lowenough to avoid any serious discoloration of the interior of theenvelope so that it is possible to observe without difficulty the bariumflash, making possible to judge the quality of the getter flash by theeye.

While I have oifered a theory of explanation as to the functioning ofthe magnesium to prevent heat losses, I do not wish to be held strictlythereto. Irrespective of any explanation, I have found it to be a factthat improved results are obtained, particularly from the standpoint ofprocessing vacuum tubes under existing factory conditions, if

to one of the electrodes or to a special support.

the getter material employed is composed of the elementsv aluminum,barium and magnesium in the percentages specified. This composition maytake the form of a true alloy of the several substances involved or analloy of barium and alum inum with the magnesium unalloyed.- In anyevent the aluminum and barium will always take the form of an alloywhile the-magnesium may be alloyed or unalloyed therewith. Forthisreason the resulting composition may be a true alloy or merely amixture. However, in certain of the claims in attempting to employ aterm sufiiciently comprehensive to include both these forms I havedesignated the composition as a getter material or a getter in the formof powdered material" and I wish it iuiderstood that these terms beinterpreted to be inclusive of both a true alloy or a mixture.

Modifications of the invention will suggest themselves to those skilledin theart but it is my intention to'cover all such modifications as comewithin the terinsof the appended claims.

What is claimed is:

1; The method of cleaning up the residual gases of an electrondevice,comprising introducing into the envelope thereoi a gettermaterial in the form 0': a powder consisting of aluminum, barium andmagnesium, the barium constituting from about 5% to about 60% and themagnesium constituting from about 1% to about 10% of the material,mechanically exhausting the envelope and first flashing the getter atthe volatilization point of the magnesium,'thereby lowering the gas"pressure within the envelope and reducing heat losses 'due'to'"convection during the completion of'the flashing operation.

2. In an electron device, a clean-up agent in the form of apellet ofpowdered material consisting of aluminum, barium and magnesium, thebarium constituting from about 5% to about 60% andthe'magnes'ium"constituting from about 1% to about 10% of thematerial.

' 3. In an electron device, a clean-up agent in the form of a'pellet ofpowdered material consisting 'of alum'inum, barium and magnesium, thealuminur'n'and barium being alloyed and the latter constituting fromabout 5% to about 60%, the magnesium being unalloyed and constitutingfrom about1% to about 10% of the material.

4. In an electron device, a clean-up agent comprising a mixtureconsisting of powdered alloy of aluminum and bariurn'having addedthereto me talliomagnesium'in powdered form, the barium constitutingfrom about 5% to about60% and the magnesium constituting from about 1%to about 10% offthe material. g p

5. The method of cleaning up the residual gases of an electron device,comprising introducinginto the envelope thereof a getter material 1 inthe form of a pellet or paste and consisting of pellet or paste form andconsisting of aluminum, barium and magnesium, the aluminum being alloyedwith the barium and present in suflioient quantity to afford stabilityto the barium when exposed to atmospheric conditions for a period oftime necessary to process a given electron device under general factoryconditions, mechanically exhausting the envelope, and first heating thegetter sufficiently to flash only the magnesium to effect a preliminaryclean-up and then heating the aluminum and barium alloy sufficiently toflash the barium only and thereby effect a final clean-up action.

7. The method of cleaning up the residual gases of an electron device,comprising introducing into the envelope a'getter material either'inpellet or paste form andconsistingof aluminum, bariumand magnesium, thealuminum beingalloyed with the barium in sufiicient quantity to affordstability to the barium when exposed to atmospheric conditions for aperiod of time necessary to process a given electron device under gen-'eral factory conditions, the amount of the magnesium being suflicient to-reduce substantially the gas pressure in the envelope but'insufficien'tto cause any serious discoloration of the interior of the envelope sothat it is possible to observe;

without difficulty, the barium fiash, and the bar-*- ium constitutingfrom about 5% to about 60% of said aluminum barium alloy.

8. The method of cleaning up the residual gases inthe envelope of anelectron discharge de-' vice which comprises introducing into the en--velope in the form of a pellet orpaste a getter material.consisting ofmagnesium mechanically mxed with a greater amount of an alloy of b'ariumand aluminum; flashing the magnesium to effect a preliminary clean up,and then flashing only the barium from said alloy to effect a finalclean up action.

9; The method of cleaning up residual gas" in the'exhausted envelopeofan electron discharge" tube whioh comprises introducing intotheenvelope a powdered getter material of Which'the major part isan alloyof barium and aluminum stable in air andthe remainder is uncombined"magnesium,nieohanically' exhausting the env lope, heatng the gettermixture 'until'magnesium from said' alloy and complete the'clean' up.

10. iAgetter material capable when fiashed'of cleaning up residual gasin the envelope of an electron discharge tube-and consisting of an al-'-loy of bar'um and'aluminum stable in air and intimately associated witha lesser amount by weight of magnesium.

11. A getter material stable for use in electron discharge tubes andconsisting of magnesium, barium and aluminum, the --ba.-- rium andaluminum being alloyed and-constitutingthe major part of said material.

1-2. A getter material for use in electron discharge tubes comprising, amixture of 11%, to

about 10% magnesium with 90% to 99% of analloy of aluminum and .barium,the barium con-m stituting from about 5% to about -60% of said. alloy.

in air and adapted.

V ,145 ERNEST ANTON LEDERER.

